What are proteins embedded in the cell membrane that facilitate the movement of ions or small molecules called?

The correct answer, ion channels, refers to specialized proteins in the cell membrane that form pores allowing ions to pass through the membrane. These channels are crucial for maintaining the cell's electrochemical gradient and enabling communication between cells. Ion channels selectively facilitate the movement of specific ions, such as sodium, potassium, calcium, or chloride, depending on the channel type and cellular needs. This selective permeability is vital for processes such as nerve impulse transmission, muscle contraction, and various signaling pathways.

Transport proteins are often confused with ion channels but encompass a broader category that includes mechanisms for moving larger molecules or ions across the membrane, sometimes requiring energy. Membrane pumps typically use ATP to actively transport ions against their concentration gradient, rather than allowing passive flow like ion channels.

Receptors, on the other hand, are proteins that bind specific ligands and initiate cellular responses but do not directly facilitate the passage of ions or molecules across the membrane. Thus, understanding the specialized role of ion channels solidifies their importance in cellular functions related to ion movement.